Electronic control systems for controlling reciprocating combustion engines typically control the ignition, the fuel injection and, if desired, certain other functions. Examples of such systems are described for instance in the U.S. Pat. Nos. 4,063,539, Gorille et al., and 4,099,495 Kienke et al, both assigned to the assignee of this application. These systems generally use a sensor which senses the rotation of the crankshaft and a computer which processes the information from the sensor to produce useful output signals which can be amplified to operate transistor switches at the proper times for obtaining the desired control of the events. The sensors are either of the segment type or the increment type, having a plurality of markers which control counting in a counting stage. Both of these sensor types are relatively complex and costly. The segment type requires a high degree of precision for the parts and their angular orientation which leads to problems in the width or angular extent of the sensor signals, with respect to shaft rotation. Also, it is difficult to maintain constant the angular spread of the signals with changes in the engine speed. The increment sensors require a plurality of marks for sensing and need additionally a reference mark and a separate pickup for it.